Lock O'Connell, who skippered the tourists in South Africa four years ago, will lead 17 new Lions out before the match at Hong Kong Stadium with Wales flanker Warburton rested after taking a knock in training.
Gatland described the injury as "slight" damage to the medial collateral ligament in his knee and scrum-half Mike Phillips said he did not expect it to keep Warburton out of the tour for long.
"He's a world class player," Phillips, who is on his second Lions tour, said of O'Connell. "It's sad for Sam but he'll be back as soon as possible."
England's Owen Farrell gets the first chance to impress at fly-half in his personal battle for the number 10 shirt with Ireland's Jonny Sexton, who is on the bench.
Otherwise, though, the backline has a distinctly Welsh feel with Jamie Roberts and Jonathan Davies pairing up in the centres, Phillips at half-back and Alex Cuthbert on one wing.
Another Welsh winger, George North, is among the replacements allowing New Zealand-born Sean Maitland a start in the back three alongside his Scotland team-mate Stuart Hogg.
Even in the absence of Warburton, the back row is an entirely Welsh unit with Toby Faletau at number eight, Justin Tipuric on the openside and Dan Lydiate wearing number six.
O'Connoll is joined in the second row by the third Scot in the tour squad, Richie Gray, behind a front row comprised of Welsh tighthead prop Adam Jones and hooker Richard Hibbard as well as England's Mako Vunipola, who will start at loosehead.
New Zealander Gatland has not started any players involved in the climax of the European season last weekend.
"We have a hard core of experience with the six former Lions sharing 430 caps between them and 19 Lions Tests," Gatland said.
"Some of the boys who played last weekend are on the bench as cover and generally everyone in the camp is raring to go."
The bench, which some believe could be the difference between the Lions and Australia come the three-Test series in June and July, has a powerful front row including Ireland's Cian Healy and experienced Lions lock Alun Wyn-Jones.
One factor heading into Saturday's match is Hong Kong's tropical heat and humidity, which can be brutal in the summer months and is expected to keep the tourists' bench active.
"With the heat and the weather, most of the guys will come off the bench," Gatland said.
Temperatures are expected to hit 33 degrees Celsius, with relative humidity to stay in the 65 percent to the 90 percent range through Saturday, according to the Hong Kong observatory.
Team: 15-Stuart Hogg, 14-Alex Cuthbert 13-Jonathan Davies, 12-Jamie Roberts, 11-Sean Maitland, 10-Owen Farrell, 9-Mike Phillips, 8-Toby Faletau, 7-Justin Tipuric, 6-Dan Lydiate, 5-Paul O'Connell (captain), 4-Richie Gray, 3-Adam Jones, 2-Richard Hibbard, 1-Mako Vunipola
Replacements: 16-Tom Youngs, 17-Cian Healy, 18-Matt Stevens, 19-Alun Wyn-Jones, 20-Jamie Heaslip, 21-Conor Murray, 22-Jonny Sexton, 23-George North
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- Mike Phillips
- Owen Farrell